This invention relates generally to a method of forming plastics and more specifically to a method of roller forming thermoplastics.
Thermoplastics have recently become available which exhibit desirable engineering characteristics heretofore unavailable in other types of plastics. Such thermoplastics, typically referred to as engineering thermoplastics, can be selected to provide high strength, impact resistance, toughness and high temperature and load bearing capabilities. These characteristics make the use of such thermoplastics particularly desirable in applications currently employing less desirable commodity plastics, or sheet metals. Such applications include, for example, large automobile body parts such as hoods, fenders and door panels.
Presently, two general types of processes are used to form thermoplastics into large parts: injection molding and sheet stamping. Each of these processes has substantial disadvantages, particularly with respect to the forming of large thin parts. Injection molding processes for thermoplastics are typically limited to parts of less than 600 square inches in surface area. This limitation is imposed by enormous clamp down forces which must be applied to mold dies to counteract large forces generated by high injection pressures acting on large part areas.
Sheet stamping processes are limited in their application to thermoplastics by the current lack of knowledge regarding large deformation behavior of the thermoplastics. This lack of knowledge regarding the large deformation behavior of thermoplastics makes it difficult to consistently produce large, high quality thermoplastic parts using currently available sheet stamping processes. Thus, such sheet stamping processes are currently limited to thermoplastic parts substantially smaller in size, for example, than those required to manufacture automobile body panels.
It would thus be desirable to provide a method for forming thermoplastic parts which reliably produces high quality parts, and which can be economically implemented using readily available technology. Such a method would be particularly useful in forming large parts from engineering thermoplastics.